Drought may be receding in Arkansas, but its deadly touch will be felt in landscapes and forests for years to come.
“County agents and extension foresters have received numerous phone calls about lawn trees dying due to insect and disease problems,” said Jon Barry, Extension forester for the University of Arkansas. “Almost all of these problems trace back to one simple factor - drought. Drought places trees under stress that may kill trees or may make trees more susceptible to insects and diseases.”
While rainfall has been much more abundant this spring than last, “this might lead landowners to conclude that trees should recover from drought. Unfortunately, this is not the case.”
Drought doesn’t just kill a tree by thirst. Drought puts the tree under chronic stress leaving it vulnerable to attacks by diseases and pests that a healthy tree could normally survive.
“The insect or disease is always present in the background but doesn’t become a problem until something puts the tree under stress,” Barry said. “Once the tree is weakened by stress, the pest attacks the tree almost always leading to tree death.”
Another way drought kills is by reducing photosynthesis in trees. To conserve water in drought, trees shed leaves, their photosynthetic engines.
“Without photosynthesis, trees don’t build adequate energy reserves to fully leaf out the following spring. Our native trees are tough and can handle drought. However, prolonged drought will deplete a tree’s energy reserves so severely that the tree may take several years to rebuild those reserves and fully leaf out again.”
Hypoxylon canker in oaks has been one of the most common problems encountered in Arkansas’ trees through the last few years. The fungus that causes hypoxylon is native to Arkansas and is always present at low levels in our forests.
“If you have seen oaks with the bark flaking off to reveal a blue-gray surface, you have seen hypoxylon canker,” Barry said. Hypoxylon is common, but it’s a weak pathogen that normally does not invade healthy trees.
However, when a tree is placed under stress by drought, “the hypoxylon fungus can colonize the tree, and once this happens, the tree will die within a few years. There is no cure for the disease.”
Pines can be attacked by several species of native bark beetles.
“Like the hypoxylon fungus, these beetles are always present in low numbers but usually kill only a few scattered pines each year,” Barry said. “However, when a drought stresses otherwise healthy trees; bark beetles, including the dreaded southern pine beetle, can attack many more trees. Even after a drought ends, trees that were damaged by the drought will continue to be susceptible to bark beetles for a few years, thus landowners should not expect tree deaths to end immediately.”
Barry recommends steps landowners can take to minimize tree deaths due to drought stress:
- Homeowners should pay attention to what they do around yard trees. With 80 percent of a tree’s roots in the top 18 inches of soil, be careful about digging around trees or compacting the soil. Avoid covering soil with fill material or an impervious surface such as a sidewalk or paved driveway.
- Give yard trees some time to recover before deciding to replace them.
- Forestland owners should maintain the vigor of forests by keeping them properly thinned. Some forestland owners are tempted to delay thinning their forest until timber prices rise. In these cases the losses due to tree pests may exceed the revenue foregone by selling timber at current prices.
For more information about hypoxylon canker see the Cooperative Extension Service publication "Hypoxylon Canker of Hardwood Shade Trees" here.
If you are having pest problems in your trees or if you would like more information about taking care of your woods, contact your county Extension agent.